This invention relates to microfluidic devices for the electrokinetic manipulation of fluidic chemical and biological materials. More specifically, this invention provides a microchip device for spatially confining and dispensing a sample material stream in a manner which lowers the axial extent of the dispensed plug.
In order to facilitate the development of the biological and chemical sciences, fluidic microchip technologies are increasingly utilized to perform traditional chemical laboratory functions within a controlled microfabricated environment. Microfabricated chemical instrumentation, also known as xe2x80x9clab-on-a-chipxe2x80x9d technology, requires the development of a plurality of microfabricated functional elements or unit processes cooperatively linked on the microchip to perform small volume chemical and biochemical measurements.
These xe2x80x9con-chipxe2x80x9d laboratories facilitate the precise transport and analysis of fluidic chemical and biological materials. The known microfluidic devices provide the advantages of reduced analysis time and reagent consumption, ease of automation, and valveless fluid control of nanoliter to sub-nanoliter volumes. A variety of electrically driven separations have been performed within microchannel networks. Microchips have also been developed for controlling chemical reactions, including arrays for solid-phase chemistry, reaction wells for polymerase chain reactions, channels with immobilized enzymes for flow injection analysis, and manifolds for homogenous enzyme assays.
The ability to design and machine channel manifolds with low-volume connections renders microchips suitable for performing several steps of an analytical process on a single device. Microchips that perform multiple chemical reactions with the speed of microscale CE analysis have been fabricated for pre- and post-separation reactions, for DNA restriction digests with fragment sizing, and for cell lysis, multiplex PCR amplification and electrophoretic sizing.
Electrokinetic techniques, i.e., electroosmotically induced fluid transport and/or electrophoretic migration of ions, are the preferred methods of manipulating biological and chemical materials on microfluidic devices. The mixing of two or more liquid-phase materials or the dispensing of a reagent material on a microchip is accomplished by controlling the electric potentials applied to the various reservoirs to electrokinetically drive the materials contained therein through the channels of the microchip. Electrophoresis transports charged species, whereas electroosmosis imparts a velocity to all ions and neutral species. Under conditions where both electroosmosis and electrophoresis are operative, the net velocity of an ion will be the vector sum of the electroosmotic and electrophoretic velocities.
Electrokinetic transport mechanisms are highly effective for effectuating a number of highly useful experiments as identified above. Several applications require the ability to spatially confine a sample material stream with consistent reproducibility. This spatial confinement or xe2x80x9celectrokinetic focusingxe2x80x9d refers to the use of electrokinetic transport to confine spatially the transport of both fluids and ions. An example of such focusing is disclosed in related U.S. Pat. No. 5,858,187, issued on Jan. 12, 1999, which describes and shows a microfluidic device and method for spatially confining a stream of fluidic material.
Further applications require the ability to dispense a volume segment of a sample material with consistent reproducibility. An example of such dispensing is disclosed in U.S. Pat. No. 5,858,195, granted Jan. 12, 1999, which describes and shows a microfluidic device and method for dispensing a volume segment of a sample material. The entire disclosure of said U.S. Pat. No. 5,858,195 is incorporated herein by reference.
More recently, a need has arisen for an improved microchip wherein the profile of the dispensed segment may be controlled to dispense more minute quantities. Examples of the benefit of shorter axial extent material segments include (i) decreasing the length required for a separation and reducing the analysis time, (ii) enabling faster axial mixing by diffusion of the segment with adjacent materials, and (iii) increasing the number of material segments per unit axial length of channel.
In accordance with one aspect of the present invention there is provided a fluidic microchip having a microchannel network for the spatial confinement of a material stream. The microchannel network includes a focusing element formed in a surface of a substrate. A sample channel is formed in the surface of the substrate for conducting a first sample fluid stream therethrough. The sample channel has a first end in fluid communication with a source of a sample fluid and a second end in fluid communication with the focusing element. A focusing channel is also formed in the surface of the substrate for conducting a focusing fluid stream therethrough. The focusing channel has a first end in fluid communication with a source of focusing fluid and a second end in fluid communication with the focusing element. A sample-waste channel formed in the surface of the substrate has a first end in fluid communication with the focusing chamber and a second end in fluid communication with a sample-waste reservoir. The fluidic microchip further includes means for driving the respective streams of the sample and focusing fluids through the respective channels into the focusing chamber, whereby the focusing fluid stream spatially confines the sample fluid stream within the focusing chamber.
In accordance with a second aspect of the present invention there is provided a fluidic microchip that is adapted for the spatial confinement of an electrokinetically driven fluidic material stream to permit dispensing of a low profile volume segment of the fluidic material. The apparatus includes a focusing element and a sample channel formed in the surface of a substrate for carrying a sample fluid stream therethrough. The device also includes a focusing channel for carrying a focusing fluid stream therethrough. In addition, the device includes a sample-waste channel for carrying a focused stream of the sample fluid stream therethrough. Further, the device includes a buffer channel for carrying a buffer fluid stream therethrough. Still further, the device includes a collection channel for carrying a volume segment of the focused stream of the sample fluid therethrough.
The sample channel, focusing channel, collection channel, buffer channel, and sample-waste channel have respective first ends in fluid communication with a source of sample fluid, a source of focusing fluid, a source of buffer fluid, a reservoir for sample waste fluid, and a reservoir for a volume segment of the sample fluid stream, respectively. The sample, focusing, buffer, sample-waste, and collection channels have their respective second ends in fluid communication with a chamber.
The buffer, sample, sample-waste, and collection channels intersect directly to form a valving element. The buffer channel and collection channel are formed such that they are positioned opposite to each other across the valving element. The focusing channel intersects the sample channel ahead of and adjacent to the valving element. The focusing channel is formed such that it is positioned more proximal to the sample fluid source than either the buffer channel or collection channel.
The apparatus may include electromotive means operatively connected to the sample fluid and the focusing fluid for (i) electrokinetically driving their respective streams of the sample and focusing fluids through their respective channels into said focusing element such that the focusing fluid stream spatially confines the sample fluid stream within the chamber and (ii) electrokinetically driving the stream of the buffer fluid through the respective channel into said valving element chamber such that a volume segment of the focused sample stream is dispensed into and transported along the collection channel.
In accordance with another aspect of the present invention there is provided a fluidic microchip having each of the features of the aforementioned first aspect of the invention with the addition of a second focusing channel. In this aspect of the device, two focusing channels are formed in the surface of said substrate for carrying focusing fluid streams therethrough. The focusing channels have respective first ends in fluid communication with a source of the focusing fluid and respective second ends in fluid communication with the focusing element. The focusing channels are formed such that they are positioned on opposite sides of the focusing element. The focusing channels are further formed such that they are positioned more proximal to the sample fluid source than either the buffer channel or collection channel.
In accordance with yet another aspect of this invention, there is provided a method for dispensing minute volume segments of the focused sample stream. The method includes the step of conducting a stream of a sample fluid through a sample fluid channel to a focusing element. In the conducting step the width of the sample fluid stream is narrowed in the focusing chamber by transporting a focusing fluid into the focusing element on one side or two opposite sides of the sample fluid stream. The method includes the further step of withdrawing a portion of the focused sample stream from the focusing chamber into the respective sample and sample-waste channels. A stream of buffer fluid is conducted through a buffer channel into the valving element such that a volume segment of the focused sample stream is dispensed into and transported along the collection channel.
Here and throughout this application, the term xe2x80x9cchamberxe2x80x9d is used to describe an area or zone that includes a xe2x80x9cfocusing elementxe2x80x9d and a xe2x80x9cvalving elementxe2x80x9d as those terms are described herein.
An alternative to electrokinetic transport mechanisms, the moving of the sample and buffer materials, and any other materials used in a device or method according to the present invention can be accomplished by application of pressure or vacuum to the appropriate channel or channels. It is also contemplated that combinations of electrokinetic, pressure, and/or vacuum transport mechanisms can be utilized in implementing a given device or method in accordance with this invention if desired.